1. Field of the Invention
The present invention relates to a method of handling liquid non-ferrous metals after smelting, and more specifically to the solid material with which the liquid material comes into contact.
2. Description of the Related Art
There is a need for refractory material that can resist the aggressive conditions that occur when the material comes into contact with liquid non-ferrous metals, such as aluminum. Among other things, this need is due to the increasing use of aluminum in vehicle parts, such as chassis and cast engine parts. Material that is to be used in direct contact with liquid aluminum must possess good corrosion properties and good erosion properties and also have a high resistance to oxidation at high temperatures and against thermal shocks, and should also have high impact resistance and high strength and hardness. The material should also be capable of being easily worked into complex shapes at a competitive cost.
The aluminum industry uses at present silicon aluminum oxynitride, SIALON, despite its high manufacturing costs. One drawback with SIALON, however, is that it is brittle and therefore expensive to work.
SiC and Si3N4 are materials that have also been evaluated in contact with liquid aluminum. It was found that Si dissolved into liquid aluminum in both cases. Si3N4 was found to have the best resistance to corrosion when produced by hot isostatic pressing (HIP) of reaction-bound Si3N4 (HIPRBSN).
A dense protective layer was formed from AlN. SiC has been found to have low corrosion resistance when the material is manufactured by using silicon metal as a binding phase. Brittleness, difficulties in mechanical working, poor resistance against thermal shocks, low impact resistance, and reactions with liquid aluminum are among the drawbacks exhibited by SiC when used with liquid aluminum.
Generally speaking, the high affinity of Al to Si and the high solubility of Si in Al normally results in Si dissolving in liquid aluminum.
Some metallic materials, such as cast iron, have normally been used in conjunction with liquid aluminum, because these metals are inexpensive, have high mechanical strength, and resist thermal shocks. Cast iron protective pipes, however, are wetted by liquid aluminum, resulting in dissolving of the material with subsequent contamination of the melt with undesirable iron particles.
The aforesaid problems are solved by the present invention.